I do believe you can use the Anvil of Generations at +8 (to go to +9).

The extra +5% +10% or +20% (depending of the Anvil used) is added on top of the actual base (with or without fortune) refine rate, so if it is 50%, then it becomes 55%, 60% or 70%.

Depending on how many equips you want to refine, or if you want to get to +13, you could also try to get a couple of refine cards for refine fortune. They multiply the refine rate by a certain percentage, with the 95 refine card multiplying this rate by 30% (of base refine rate, not together with Anvils) each time is chosen (so up to 90%). There are other refine cards, cheaper but have a smaller refine rate increase.

For example, if the base refine rate is 50%, with one refine 95 fortune card chosen the final refine rate becomes 65% without Anvils (80% for 2, and if you managed the rare 3, 95%). They work for all levels, unlike Anvils, as well.